U.S. patent number 5,924,888 [Application Number 08/881,335] was granted by the patent office on 1999-07-20 for electrical plug.
This patent grant is currently assigned to Raychem Corporation. Invention is credited to Brian S. Larkin.
United States Patent |
5,924,888 |
Larkin |
July 20, 1999 |
Electrical plug
Abstract
An electrical plug for connecting an electrical cable such as an
electrical heating cable to an electrical power outlet. Contained
within the housing of the plug are first and second contact members
which comprise a first prong and a second prong, respectively, each
prong being suitable for insertion into a socket of an electrical
power outlet. A cutting module and a cutting element which fits
within the cutting module are used to remove polymer, e.g.
insulation or a conductive polymer composition, from the first and
second electrodes of the cable at the end of the cable in order to
make electrical connection from the electrodes to the first and
second contact members. Present within the cutting module are first
and second electrode-contact sections positioned on the concave
arcuate inner surface of the wall of a cavity in the cutting
module. The electrode-contact sections can be electrically
connected to the first and second contact members. The cutting
element comprises a cutting wedge which has (a) a convex arcuate
outer surface which complements the inner surface of the wall of
the cutting module, and (b) piercing means suitable for penetrating
the polymer. The cutting element rotates within the cavity of the
cutting module from an opened position to a closed position so
that, after the cable has been inserted into the cavity and the
cutting element is rotated, the rotation first causes the piercing
means to penetrate the polymer between the first and second
electrodes, then causes an end portion of the polymer to separate
from the electrodes, and then forces the first electrode into
physical contact with the first electrode-contact section and the
second electrode into physical contact with the second
electrode-contact section. The cutting module and the cutting
element can also be used as a tool for removing polymer from an
electrical cable, and in a connector to make electrical connection
from a first electrical cable to a second electrical cable.
Inventors: |
Larkin; Brian S. (Moss Beach,
CA) |
Assignee: |
Raychem Corporation (Menlo
Park, CA)
|
Family
ID: |
24349793 |
Appl.
No.: |
08/881,335 |
Filed: |
June 24, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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587433 |
Jan 17, 1996 |
5718600 |
Feb 17, 1998 |
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Current U.S.
Class: |
439/410;
439/696 |
Current CPC
Class: |
H01R
4/2491 (20130101); H01R 13/68 (20130101); H01R
24/30 (20130101); H01R 13/7135 (20130101); H01R
4/5083 (20130101); H01R 13/582 (20130101); H01R
13/58 (20130101); H01R 2103/00 (20130101); H01R
4/5008 (20130101) |
Current International
Class: |
H01R
4/24 (20060101); H01R 13/58 (20060101); H01R
13/713 (20060101); H01R 4/50 (20060101); H01R
13/70 (20060101); H01R 13/68 (20060101); H01R
004/26 () |
Field of
Search: |
;439/410,417,695,696,697,687 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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456713 |
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Jul 1968 |
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CH |
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WO 91/05377 |
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Apr 1991 |
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WO |
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WO 91/17642 |
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Nov 1991 |
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WO |
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WO 96/35242 |
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Nov 1996 |
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WO |
|
Primary Examiner: Stephan; Steven L.
Assistant Examiner: Biggi; Brian J.
Attorney, Agent or Firm: Gerstner; Marguerite E. Burkard;
Herbert G.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of commonly
assigned application Ser. No. 08/587,433, filed Jan. 17, 1996, now
U.S. Pat. No. 5,718,600, issued Feb. 17, 1998, the disclosure of
which is incorporated herein by reference.
Claims
What is claimed is:
1. An electrical plug for connecting an electrical cable to an
electrical power outlet, said electrical cable comprising a first
elongate electrode and a second elongate electrode, said first and
second electrodes surrounded by and separated from one another by a
polymer, said plug comprising
(A) a housing which comprises
(1) a first housing member which comprises a slot for receiving the
cable, and
(2) a second housing member,
the first and second housing members being movable relative to each
other between a unique mated configuration and a demated
configuration;
(B) a first contact member which comprises a first prong suitable
for insertion into one socket of an electrical power outlet;
(C) a second contact member which comprises a second prong suitable
for insertion into a second socket of an electrical power
outlet;
(D) a cutting module which is positioned in the first housing
member and which comprises
(1) a cavity comprising a wall which has a concave arcuate inner
surface,
(2) an opening in the wall which opens into the cavity and is
aligned with the slot for receiving the cable,
(3) a first electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
first prong, and
(4) a second electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
second prong; and
(E) a cutting element which
(1) fits within the cutting module,
(2) comprises a cutting wedge which comprises
(a) a convex arcuate outer surface which complements the inner
surface of the wall,
(b) piercing means suitable for penetrating the polymer, and
(c) first and second grooves which are (i) parallel to one another,
(ii) positioned on the convex outer surface, and (iii) positioned
one on either side of the piercing means; and
(3) rotates within the cavity from an opened position to a closed
position so that, after the cable has been inserted into the cavity
through the opening and the cutting element is rotated, the
rotation
(a) first, causes the piercing means to penetrate the polymer
between the first and second electrodes,
(b) second, causes an end portion of the polymer to separate from
the electrodes, and
(c) third, forces the first electrode into physical contact with
the first electrode-contact section and the second electrode into
physical contact with the second electrode-contact section.
2. A plug according to claim 1 wherein
(1) the cutting element comprises a recess suitable for receiving a
lever, and
(2) the second housing member comprises a locking bar on an inner
surface, which, when the cutting element is in the closed position,
mates with the recess.
3. A plug according to claim 2 wherein the second housing member
comprises first and second sections which are separated from one
another.
4. A plug according to claim 3 wherein the second section comprises
the locking bar.
5. A plug according to claim 3 which further comprises means for
strain relief.
6. A plug according to claim 1 in which the first electrode-contact
section and the second electrode-contact section are electrically
connected to a circuit interrupting device.
7. A plug according to claim 6 wherein the circuit interrupting
device is a ground fault circuit interrupter or a ground fault
equipment protection circuit interrupter.
8. A plug according to claim 1 which further comprises a fuse
electrically connected to the first contact member and the second
contact member.
9. A plug according to claim 1 wherein the cutting module further
comprises a ground-contact section into which a grounding element
can be placed.
10. A plug according to claim 1 wherein the cable is an elongate
heating cable which comprises
(A) first and second elongate wire electrodes,
(B) a plurality of resistive heating elements connected in parallel
between said electrodes, and
(C) an insulating jacket which surrounds the electrodes and heating
elements.
11. A plug according to claim 10 wherein the cable further
comprises a metallic grounding layer in the form of a braid or a
tape.
12. A plug according to claim 1 wherein the piercing means
comprises an electrically insulating material.
13. A connector for connecting an end of a first elongate
electrical cable to an end of a second elongate electrical cable,
said first cable comprising first and second elongate electrodes
surrounded by and separated from one another by a first polymer,
and said second cable comprising third and fourth elongate
electrodes surrounded by and separated from one another by a second
polymer, said connector comprising
(A) a housing which comprises
(1) a first housing member which comprises a first slot for
receiving the first cable, and
(2) a second housing member,
the first and second housing members (a) being movable relative to
each other between a unique mated configuration and a demated
configuration, and (b) when mated comprising an opening for
receiving the second cable;
(B) a first connection means for connecting the first electrode to
the third electrode within the housing;
(C) a second connection means for connecting the second electrode
to the fourth electrode within the housing;
(D) a cutting module which is positioned in the first housing
member and which comprises
(1) a cavity comprising a wall which has a concave arcuate inner
surface,
(2) an opening in the wall which opens into the cavity and is
aligned with the first slot for receiving the first cable,
(3) a first electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
first connection means, and
(4) a second electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
second connection means; and
(E) a cutting element which
(1) fits within the cutting module,
(2) comprises a cutting wedge which comprises
(a) a convex arcuate outer surface which complements the inner
surface of the wall,
(b) piercing means suitable for penetrating the first polymer,
and
(c) first and second grooves which are (i) parallel to one another,
(ii) positioned on the convex outer surface and (iii) positioned
one on either side of the piercing means; and
(3) rotates within the cavity from an opened position to a closed
position so that, after the first cable has been inserted into the
cavity through the opening and the cutting element is rotated, the
rotation
(a) first, causes the piercing means to penetrate the first polymer
between the first and second electrodes,
(b) second, causes an end portion of the first polymer to separate
from the first and second electrodes, and
(c) third, forces the first electrode into physical contact with
the first electrode-contact section and the second electrode into
physical contact with the second electrode-contact section.
14. A connector according to claim 13 wherein the first cable and
the second cable are elongate heating cables.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrical plugs, particularly electrical
plugs which are useful for making an electrical connection between
an elongate electrical cable and an electrical power outlet.
2. Introduction to the Invention
It is often necessary to make an electrical connection from an
elongate cable such as a power cord, a grounded power lead, or
heating cable to another elongate cable or to a source of
electrical power such as a wall outlet. Connection to a power
source is frequently made by means of an electrical plug.
Connection of the cable to the plug often requires tedious and
craft-sensitive assembly, as well as the use of special tools, in
order to ensure that good electrical connection is achieved.
Elongate heating cables are one type of cable which often requires
connection to a plug. Such heating cables are known for use in the
freeze protection and temperature maintenance of pipes.
Particularly useful elongate heating cables comprise (a) first and
second elongate electrodes, (b) a plurality of resistive heating
elements connected in parallel between said electrodes, e.g. a
continuous strip of a conductive polymer in which the electrodes
are embedded or which is wrapped around the electrodes, and (c) an
insulating jacket which surrounds the electrodes and heating
elements. In addition, the heating cable often also comprises a
metallic grounding layer, in the form of a braid or a tape,
surrounding the insulating jacket, which serves to electrically
ground the heating cable and provides abrasion resistance. The
heating cable may be cut to the appropriate length for use in each
application, and connection must then be made to the plug.
Conventional electrical plugs for use with heating cables often
require that, prior to installation of the cable into the plug, the
conductive polymer must be stripped from the electrodes. Such an
electrical plug is disclosed in U.S. Pat. Nos. 5,002,501 (Tucker)
and 5,004,432 (Tucker), the disclosure of which is incorporated
herein by reference. Stripping the polymer can be difficult, may
require special tools, and may not result in completely "clean"
electrodes, thus making good electrical connection to the plug
difficult. In addition, the time required to strip the polymer and
assemble the plug is relatively high. U.S. Pat. No. 5,252,081
(Hart) discloses a plug in which the electrode need not be stripped
prior to insertion of the cable into the plug. Connection to the
electrodes is made with conductive piercing means which penetrate
the insulating jacket and the conductive polymer, thus contacting
the electrodes. In order to make adequate contact, it is necessary
that the piercing means, e.g. screws, be sufficiently tightened. In
addition, it is important that the dimensional tolerance be precise
to ensure that the screws directly contact the electrodes and
maintain good electrical connection even after creep and/or aging
of the polymer and electrodes.
SUMMARY OF THE INVENTION
We have now found that it is possible to make an easy, reliable
connection to an electrical cable without stripping the polymeric
insulation from the electrodes and without the need for using
screws or other means of penetrating the insulation to precisely
contact the electrodes. By the use of our invention it is possible
to insert an electrical cable into the plug, rotate a cutting
element, e.g. 90.degree., to remove the surrounding polymer and
ensure contact of the electrodes with the electrical contacts, and
lock the cable into position to provide adequate strain relief. No
special tools are required. Thus, in a first aspect this invention
provides an electrical plug for connecting an electrical cable to
an electrical power outlet, said electrical cable comprising a
first elongate electrode and a second elongate electrode, said
first and second electrodes surrounded by and separated from one
another by a polymer, said plug comprising
(A) a housing which comprises
(1) a first housing member which comprises a slot for receiving the
cable, and
(2) a second housing member,
the first and second housing members being movable relative to each
other between a unique mated configuration and a demated
configuration;
(B) a first contact member which comprises a first prong suitable
for insertion into one socket of an electrical power outlet;
(C) a second contact member which comprises a second prong suitable
for insertion into a second socket of an electrical power
outlet;
(D) a cutting module which is positioned in the first housing
member and which comprises
(1) a cavity comprising a wall which has a concave arcuate inner
surface,
(2) an opening in the wall which opens into the cavity and is
aligned with the slot for receiving the cable,
(3) a first electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
first prong, and
(4) a second electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
second prong; and
(E) a cutting element which
(1) fits within the cutting module,
(2) comprises a cutting wedge which comprises
(a) a convex arcuate outer surface which complements the inner
surface of the wall, and
(b) piercing means suitable for penetrating the polymer, and
(3) rotates within the cavity from an opened position to a closed
position so that, after the cable has been inserted into the cavity
through the opening and the cutting element is rotated, the
rotation
(a) first, causes the piercing means to penetrate the polymer
between the first and second electrodes,
(b) second, causes an end portion of the polymer to separate from
the electrodes, and
(c) third, forces the first electrode into physical contact with
the first electrode-contact section and the second electrode into
physical contact with the second electrode-contact section.
We have also discovered that particular components that are part of
the electrical plug described in the first aspect of the invention
are themselves useful, either as part of a connector or other
device or by themselves. For example, we have found that a cutting
module and a cutting element can be used as a tool for stripping
insulation, e.g. polymer, from an electrical cable, including an
insulated wire. Thus in a second aspect, this invention provides a
tool for removing polymer from an electrical cable comprising a
first elongate electrode surrounded by polymer, said tool
comprising
(A) a cutting module which comprises
(1) a cavity comprising a wall which has a concave arcuate inner
surface, and
(2) an opening in the wall which opens into the cavity for
receiving the cable; and
(B) a cutting element which
(1) fits within the cutting module,
(2) comprises a cutting wedge which comprises
(a) a convex arcuate outer surface which complements the inner
surface of the wall, and
(b) piercing means suitable for penetrating the polymer, and
(3) rotates within the cavity so that, after the cable has been
inserted into the opening and the cutting element is rotated, the
rotation first causes the piercing means to penetrate the polymer,
and then causes an end portion of the polymer to separate from the
electrode.
The cutting module and cutting element can also be used in a
connector which makes an electrical connection between two or more
elongate cables. Thus in a third aspect, the invention provides a
connector for connecting an end of a first elongate electrical
cable to an end of a second elongate electrical cable, said first
cable comprising first and second elongate electrodes surrounded by
and separated from one another by a first polymer, and said second
cable comprising third and fourth elongate electrodes surrounded by
and separated from one another by a second polymer, said connector
comprising
(A) a housing which comprises
(1) a first housing member which comprises a first slot for
receiving the first cable, and
(2) a second housing member,
the first and second housing members (a) being movable relative to
each other between a unique mated configuration and a demated
configuration, and (b) when mated comprising an opening for
receiving the second cable;
(B) a first connection means for connecting the first electrode to
the third electrode within the housing;
(C) a second connection means for connecting the second electrode
to the fourth electrode within the housing;
(D) a cutting module which is positioned in the first housing
member and which comprises
(1) a cavity comprising a wall which has a concave arcuate inner
surface,
(2) an opening in the wall which opens into the cavity and is
aligned with the first slot for receiving the first cable,
(3) a first electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
first connection means, and
(4) a second electrode-contact section which is positioned on the
inner surface of the wall and can be electrically connected to the
second connection means; and
(E) a cutting element which
(1) fits within the cutting module,
(2) comprises a cutting wedge which comprises
(a) a convex arcuate outer surface which complements the inner
surface of the wall, and
(b) piercing means suitable for penetrating the first polymer,
and
(3) rotates within the cavity from an opened position to a closed
position so that, after the first cable has been inserted into the
cavity through the opening and the cutting element is rotated, the
rotation
(a) first, causes the piercing means to penetrate the first polymer
between the first and second electrodes,
(b) second, causes an end portion of the first polymer to separate
from the first and second electrodes, and
(c) third, forces the first electrode into physical contact with
the first electrode-contact section and the second electrode into
physical contact with the second electrode-contact section.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by the drawings in which FIG. 1 is a
perspective schematic drawing of an electrical plug of the
invention;
FIGS. 2 and 3 show in perspective schematic view the housing
components of the electrical plug of the invention;
FIG. 4 shows in perspective schematic view a component of the
cutting module component of the electrical plug of the
invention;
FIG. 5 shows in perspective schematic view a housing component of
the electrical plug of the invention;
FIG. 6 shows in perspective schematic view a cutting element
component of the electrical plug of the invention;
FIG. 7 shows in plan view the cutting element of FIG. 6;
FIG. 8 shows in perspective schematic view another cutting element
component of the electrical plug; and
FIGS. 9 and 10 show in plan view two views of the cutting element
of FIG. 8 .
DETAILED DESCRIPTION OF THE INVENTION
The electrical plug of the invention is designed to connect an
elongate electrical cable to an electrical power outlet, e.g. a
wall outlet. The electrical cable may comprise a heating cable, a
power cable or cord, a grounded power lead, or other type of cable.
Elongate electrical heating cables appropriate for use with this
plug are those which comprise first and second elongate electrodes,
a plurality of resistive heating elements comprising a polymer
connected in parallel between the electrodes, and at least one
insulating jacket surrounding the electrodes and heating elements.
The insulating jacket is generally polymeric, in the form of a
continuous polymer layer, although a polymeric braid or a polymer
tape may be used. For some applications a polymeric insulating
jacket is surrounded by a second layer, e.g. a second polymeric
insulating layer such as a polyester tape, or a metallized tape
such as aluminized polyester. The heating cable often comprises an
optional metallic grounding braid surrounding the insulating jacket
and the optional second layer. The metallic grounding braid serves
to electrically ground the heating cable and also provides
mechanical strength and abrasion resistance. When a metallic
grounding braid is present, it generally is in the form of braided
metal wires, although for applications in which flexibility is not
critical, it is possible to use another type of metal layer, e.g. a
sheath or metal tape. In this specification, the term "metallic
grounding braid" is intended to include non-braided metal layers.
In some applications, the grounding braid itself is surrounded by
an insulating jacket to provide environmental and electrical
insulation to the heating cable. Particularly suitable heating
cables are self-regulating strip heaters in which the electrodes
are elongate wires and the heating elements comprise a conductive
polymer composition which exhibits PTC (positive temperature
coefficient of resistance) behavior. Heaters of this type are
described in U.S. Pat. Nos. 3,858,144 (Bedard et al), 3,861,029
(Smith-Johannsen et al), 4,017,715 (Whitney et al), 4,242,573
(Batliwalla), 4,334,148 (Kampe), 4,334,351 (Sopory), 4,426,339
(Kamath et al), 4,459,473 (Kamath), 4,574,188 (Midgley et al), and
5,111,032 (Batliwalla et al), and International Patent Publication
No. WO91/17642 (Raychem Corporation, published Nov. 14, 1991). The
disclosure of each of these patents and publications is
incorporated herein by reference. The heating cable generally has
an approximately rectangular cross-section with two generally
parallel faces, although other geometries, e.g. round, oval, or
elliptical, can also be used.
In a second aspect, the invention provides a tool for removing
polymer from an electrical cable. The cable can be the same type as
those used in the electrical plug, although other types of cable,
in which there is a single elongate electrode surrounded by
polymer, generally an insulating polymer, may be used.
In a third aspect, which provides a connector for making an
electrical connection between the ends of first and second elongate
electrical cables, the first cable comprises first and second
elongate electrodes surrounded by and separated from one another by
a first polymer, and the second cable comprises third and fourth
elongate electrodes surrounded by and separated from one another by
a second polymer. The first and second cables may be the same type
as those used in the electrical plug. One or both may also comprise
a metallic grounding braid.
The plug comprises a housing which comprises first and second
housing members which are capable of existing in a demated or a
unique mated configuration. In the demated configuration, the
housing members may be separate pieces or they may be connected,
e.g. by hinges. When mated, the housing members are in contact with
each other, either directly or indirectly through a sealing member
such as a gasket. The housing members are maintained in their mated
configuration by means of a securing means, e.g. a strap, a latch,
a spring clamp, a bracket, one or more screws, or integral snaps.
The securing means may be removable in order to allow the housing
members to be demated from one another and allow the plug to be
reenterable. In a preferred embodiment, the securing means
comprises screws which, when tightened after insertion of the
cable, ensure that good electrical contact is achieved and
maintained.
The first housing member is generally a single piece which may be
compartmentalized, either by ribs or bosses, or nominally, for
various functions. At one end of the first housing member is a slot
for receiving the cable. The slot generally conforms in shape to
the cable and has a size slightly larger than the cable (without
any metallic ground braid or outer insulating jacket) to make
insertion easy. The first housing member should be large enough to
accommodate the cutting module and strain relief means (generally
both in one compartment), as well as any circuit interrupting
device, signal indicator, fuse, or other element (generally all in
a second compartment).
The second housing member may be a single piece which may be
compartmentalized, but it often comprises two or more sections
which are separated from one another. In a preferred embodiment,
the second housing member comprises a first section containing the
first and second contact members, as well as other electrical
components (e.g. circuit interrupting device, signal indicator,
fuse), and a second section which comprises a locking bar on an
inner surface which can be used to mate with a recess on the
cutting element when it is in closed position. The first section
often is secured in a permanent fashion to the first housing member
before installation of the cable, while the second section can be
readily removed and replaced.
Positioned within the first housing member is a cutting module
which comprises a cavity having a wall. In a preferred embodiment,
the wall has a concave arcuate inner surface which has an opening
which opens into the cavity and is aligned with the slot for
receiving the cable. Fitting within the cutting module is a cutting
element which comprises a cutting wedge. The cutting wedge
preferably comprises a convex arcuate outer surface which
complements the inner surface of the wall. Piercing means suitable
for penetrating the polymer are part of the cutting wedge, either
as an integral part of the cutting wedge or as a separate part. The
cutting wedge can rotate within the cavity from an opened position
to a closed position, preferably a unique closed position, so that,
after the cable has been inserted into the opening and the cutting
element is rotated, the rotation first causes the piercing means to
penetrate the polymer (between the first and second electrodes),
then causes an end portion of the polymer to separate from the
electrodes. The rotation may be any appropriate amount, but for
many applications it is preferred that the rotation be 90.degree.
from the opened to the closed position. To assist in the rotation,
the cutting element may comprise a recess suitable for receiving a
lever, e.g. a screwdriver, which allows an increase in torque
applied to the cable. This recess can be mated with the locking bar
on the second housing member to ensure that the cutting element is
fully closed. It is preferred that the cutting wedge have an inner
surface which is convex such that the wedge has an increasing
thickness in a direction away from the piercing means. This means
that when the piercing means penetrates the polymer, and the wedge
is forced into the polymer by the rotation of the cutting element,
an increasing force is applied. If, as is preferred, the cutting
wedge has a triangular shape, in which the piercing means is one
point of the triangle, an increasing width of the wedge is forced
into the polymer during rotation, aiding in the separation of the
polymer from the electrodes and ensuring that the electrodes stay
apart from one another. The piercing means, and preferably the
cutting wedge, are electrically insulating. The shape of the
cutting wedge depends on the differential hardness of the
electrodes and the polymer. It is necessary that the polymer be
separated from the electrodes without shearing the electrodes. In a
preferred embodiment, the piercing means has an angle of 30 to
60.degree., preferably 40 to 50.degree., e.g. 45.degree.. The angle
is determined as the complementary angle of the intersection of a
center line of the recess and a tangent from the inside radius of
the piercing means, as shown in FIG. 7 hereinafter. In addition,
the cutting wedge may also comprise an arcuate rib disposed on the
outer convex surface of the cutting wedge to maintain separation of
the electrodes as the cutting element is rotated into the closed
position. This rib may be positioned at any height on the cutting
wedge outer surface, but it is preferred that it be at a height in
line with the piercing means. The end portion of the polymer, which
may comprise more than one material, e.g. a conductive polymer
layer and an insulating polymer layer, is preferably retained in a
cavity formed by the cutting wedge and a wall of the cutting
module.
In a preferred embodiment, two grooves, preferably parallel
grooves, are incorporated into the outer surface of the cutting
wedge, positioned on either side of the piercing means and parallel
to the top and bottom surfaces of the cutting element. The grooves
are preferably parallel to assist in guiding the alignment of the
electrodes. The grooves may be molded or cut, or otherwise formed,
in the outer surface of the cutting wedge. The dimensions of the
grooves are determined by the size of the electrodes and the
spacing between the electrodes, but, in general, the width and
depth of the grooves are larger, e.g. at least 5% larger, than the
diameter of the electrodes. For example, grooves with a width of 1
mm (0.040 inch) and a depth of 1 mm (0.040 inch) are suitable for
use with 22 AWG stranded electrodes having a diameter of about 0.8
mm (0.03 inch). The grooves are particularly useful when the
elongate cable is to be installed at a low temperature, e.g.
0.degree. C., at which the polymer is stiff. Under normal
conditions, when the polymer is flexible, the piercing means makes
contact with the cable and, as the cutting element is rotated, the
cable is bent in the direction of rotation. The piercing means
penetrates the polymer (both the insulating jacket, if present, and
the polymer surrounding the electrodes) and displaces the polymer
from the electrodes. As the rotation is completed, the first and
second electrodes are forced into contact with the first and second
electrode-contact sections, respectively. When the temperature is
low, the stiffness of the polymer prevents it from bending during
the initial part of the rotation, and the piercing means acts to
cut the wire electrodes, rather than merely displace the polymer.
The grooves adjacent to the piercing means provide space for the
electrodes to be positioned, out of the cutting path of the
piercing means. As the rotation continues, the polymer does
eventually bend and the end portion of the polymer is removed.
It is important that electrical connection be made to the cable
when it is installed into the plug. The plug comprises a first
contact member which comprises a first prong suitable for insertion
into one socket of an electrical power outlet and a second contact
member which comprises a second prong suitable for insertion into a
second socket of an electrical power outlet. Both the first and
second contact members are positioned in the second housing member,
generally protruding through the wall of the second housing member.
A first electrode-contact section is positioned on the inner
surface of the wall of the cutting module and can be electrically
connected to the first contact member by means of a wire, solder or
metal trace or other means. A second electrode-contact section is
also positioned on the inner surface of the wall of the cutting
module and can be electrically connected to the second contact
member by means of a wire, solder or metal trace, or other means.
The first and second electrode-contact sections are generally in
the form of a brass, copper, or other metal terminal which can be
attached to the appropriate position on the wall by means of
screws, adhesive, tacks, or other means. The first and second
electrode-contact sections are electrically isolated from one
another and are physically separated, generally by a distance
slightly less than the distance separating the first and second
electrodes. When the cutting element is rotated in the cavity, and
after the end portion of polymer is separated from the electrodes,
the rotation forces the first electrode into physical contact with
the first electrode-contact section and the second electrode into
the second electrode-contact section. The presence of the cutting
wedge maintains the separation of the electrodes, and the force of
the cutting element against the wall of the cutting module
maintains the first and second electrodes in contact with the
appropriate electrode-contact section.
It is particularly preferred that the plug comprise additional
electrical components for added functionality and safety. Thus in a
preferred embodiment, a fuse is electrically connected to the first
contact member and the second contact member. Suitable fuses for
use with plugs designed for 120 volt applications include those
which have a 7 ampere/125 volt rating, such as those sold under the
name Picofuse.TM. 7A/125V by Littelfuse Inc. or those sold under
the name Microtron.TM. fuse MCR-7 by Bussman Division of Cooper
Industries. It is also preferred that the first electrode-contact
section and the second electrode-contact section be electrically
connected to a circuit interrupting device, which may be a ground
fault circuit interrupter (GFCI) or a ground fault equipment
protection circuit interrupter (GFEPCI). A GFCI with a rating of 5
mA can be used when personnel shock protection is desired, while an
8 mA-rated GFEPCI can be used to provide ground fault protection of
equipment. Particularly preferred is the use of a GFEPCI with a
non-replaceable fuse, such as that sold by Tower Switches Ltd.
(catalog number 3033). In addition, a signal indicator, e.g. a
light, may be electrically connected, e.g. to the fuse or to
another component, for various purposes, e.g. to indicate if power
is applied to plug or if the fuse has tripped.
The cable often comprises a metallic grounding braid, and in a
preferred embodiment, the plug comprises a third contact member
which comprises a third prong suitable for insertion into the
ground socket of an electrical power outlet, and a ground-contact
section into which a grounding element, e.g. the braid, can be
placed. The ground-contact section may be positioned in the cutting
module, outside of the cavity and adjacent the slot, and comprises
a metallic clip or other attachment means which is electrically
connected to the third contact member by means of a wire, solder or
metal trace, or other means. In use, the metallic grounding braid
is folded back from the end of the cable, and twisted to form a
tail. The cable is then inserted into the plug to position it
within the cavity. The tail is inserted into or otherwise attached
to the clip, making physical and electrical connection.
For many embodiments of the plug, also present is a means for
strain relief. When making a connection of the cable into the plug,
it is important that the cable be held in position with sufficient
strength so that it cannot readily be pulled out of the plug.
Generally a "pullout force" of at least 25 pounds (11.4 kg),
preferably at least 30 pounds (13.6 kg), particularly at least 35
pounds (15.9 kg) is required for routine use. The pullout force can
be measured according to a test in which a known weight, e.g. 15.9
kg (35 pounds), is hung on the end of the cable (following
insertion into the plug) at an angle of 180.degree. for one minute.
The weight is then removed and the cable measured to determine if
any slippage from the plug, or cutting or tearing of the cable, has
occurred. If no damage or slippage is observed, the pullout force
is said to be at least as great as the known weight. The strain
relief means allows adequate pullout force to be generated when the
cable is installed in the plug. In a preferred embodiment the
strain relief means comprises a first strain relief element in the
form of a rib and a second strain relief element in the form of a
tab. The first strain relief element is part of the first housing
member, and is generally spaced in line with and behind the slot,
so that an inserted cable, without the presence of the second
housing member, will contact both an edge of the slot and the rib.
The second strain relief element is part of the second housing
member, preferably part of the second section of the second housing
member, and is designed so that when the second housing member is
mated with the first housing member, the second strain relief
member is adjacent to the slot and at least partially covers the
slot. This means that when the cable is inserted into the slot, and
the second housing member is mated with the first housing member,
the cable is forced into a serpentine configuration between the
slot, the second strain relief element (e.g. the tab) and the first
strain relief element (e.g. the rib). In a preferred configuration,
the rib is generally U-shaped and forms a channel with the slot for
insertion of the cable.
The tool of the second aspect of the invention comprises a cutting
module and cutting element as described above. A housing comprising
one or more members may be present.
In the third aspect of the invention, elements described above
primarily in terms of a plug can be used to make an electrical
connection between a first elongate electrical cable, e.g. a
heating cable, and a second elongate electrical cable. The first
and second cables may be the same or different depending on the
type of connection to be made. The housing of the connector
comprises an opening for receiving the second cable when the first
and second housing members are mated. If three or more cables are
to be connected, additional openings may be present. It is possible
that the first housing member may comprise a second slot for
receiving the second cable. Depending on the type of connection to
be made, the second slot may be at the opposite end of the first
housing member from the slot for the first cable (i.e. the first
slot), or it may be located on a side perpendicular to that
containing the first slot. Additional slots may be added as
necessary.
The first electrode of the first cable is electrically connected to
the third electrode of the second cable by means of a first
connection means and the second electrode of the first cable is
electrically connected to the fourth electrode of the second cable
by means of a second connection means. Both first and second
connection means are within the housing, generally within the first
housing member, and may be any suitable type of element, e.g. a
crimp, a terminal block, or an insulation displacement connector
(IDC). Suitable connection means for connecting to a ground may
also be present. While a single cutting module and cutting element
may be present, it is possible that the connector may comprise two
or more cutting modules and cutting elements, one for removing the
insulation from each inserted cable.
Depending on the exact configuration of the connector, the type of
cables, and the electrical connections in the connector, possible
connections include a splice between two heating cables, a power
connection between the heating cable and a power cable, a "tee"
connecting the heating cable to two other heating cables, a cross
in which four heating cables are connected, a powered splice in
which the heating cable is connected to another heating cable and
to a power cable, and a powered tee in which a power cable is
connected to the heating cable as well as two other heating
cables.
The housing members, the cutting module, the cutting element and
other structural elements of the plug, tool, or connector may
comprise an insulated metal or ceramic but preferably comprise a
polymer which has an impact strength of at least 5 foot-pounds when
shaped into the particular element and measured by such tests as UL
746C. Depending on the desired use conditions and the type of cable
used, it may be desirable to use different materials for different
parts of the plug or tool, e.g. polymeric housing members and
cutting modules, but a ceramic cutting element. Preferred polymers
are of light weight, can be shaped by injection- or
transfer-molding or similar processing techniques, and will
withstand required intermittent use and continuous use
temperatures. Appropriate polymers include polycarbonate, nylon,
polyester, polyphenylene sulfide, polyphenylene oxide, and other
engineering plastics. Appropriate fillers and stabilizers may be
present. To improve the impact strength of the plug or tool,
internal elements such as ribs and bosses and external elements
such as grooves may be incorporated into the design of the various
elements.
While the cutting module and the cutting element have been
described as having complementary arcuate surfaces, it is possible
that a wedge-shaped cutting element, which could slide along a
track, rather than rotate, could be used to strip polymer from an
electrode and/or make an appropriate electrical connection.
The invention is described by the drawings in which FIG. 1 shows in
perspective electrical plug 1 of the invention when fully
assembled. Housing 3 is formed from first housing member 5, first
section 7 of second housing member and second section 9 of second
housing member which are secured by screws (not shown). Inserted
into slot 23 is electrical cable 11. First contact member 13,
second contact member 15, and third contact member 17, each in the
form of a prong, are seen.
FIGS. 2 and 3 show first housing member 5 in perspective view. Also
shown in exploded view in FIG. 2 is second section 9 of second
housing member. First housing member 5 has two compartments 19,21.
First compartment 19 is large enough for insertion of the necessary
electronic components, e.g. a GFEPCI and a fuse, not shown.
Openings in first compartment 19 allow insertion of various other
elements: e.g. a signal light can be positioned in opening 53 and a
reset button positioned in opening 55. Second compartment 21
contains slot 23 and cutting module 25. Contained within cutting
module 25 are cavity 27 which has a concave arcuate inner surface
on wall 29, and opening 31 which is aligned with slot 23. First
electrode-contact section 33 is present on top of the wall 29, and
folds over into cavity 27, as well. Cutting element 37 is shown in
open position in FIG. 2, in which recess 39 is perpendicular to
slot 23, and in closed position in FIG. 3, in which recess 39 is
aligned with slot 23. When in the closed position, cutting element
37 forms pocket 41 for containment of the polymer which has been
separated from the cable. Ground contact section 43 and pocket 45
for containing a ground lead are also present on cutting module 25.
First strain relief element 47, in the shape of a rib, is
positioned adjacent and spaced away from slot 23. Shown on second
section 9 of second housing member in FIG. 2 is second strain
relief element 49 in the form of a tab. Securing means 51, e.g.
screws, allow second section 9 of second housing member to be
attached to second compartment 21 of first housing member 5.
FIG. 4 shows cutting module 25 without cutting element 37. Cavity
27, opening 31, and wall 29 with a concave arcuate surface are
visible. Also shown are first electrode-contact region 33, second
electrode-contact region 35, and ground contact section 43.
FIG. 5 shows the interior of second section 9 of second housing
member. Visible are second strain relief element 49 and locking bar
57.
FIGS. 6 and 7 show cutting element 37, including recess 39. Cutting
wedge 59, of generally triangular shape, has piercing means 61 at
one point of the triangle, and has a convex inner surface 63.
Convex outer surface 65 complements wall 29 with a concave arcuate
surface. Mounting pin 67 can be inserted into cutting module 25,
allowing cutting element 37 to rotate. Angle A, for this cutting
wedge is about 45.degree., and is shown as the complementary angle
of the intersection of a center line of recess 39 and a tangent
from the inside radius of piercing means 61.
FIGS. 8 to 10 show cutting element 37 in different orientations. In
contrast to the cutting element of FIGS. 6 and 7, cutting wedge 59
of cutting element 37 in FIGS. 8 to 10 comprises first groove 71
and second groove 73 positioned on opposite sides of piercing means
61. First and second grooves 71,73 are parallel to one another.
Also shown in FIGS. 9 and 10 is arcuate rib 75 which is positioned
at a height on convex outer surface 65 approximately the same as
piercing means 61 and between the height of first and second
grooves 71,73.
Although the invention has been described in detail for specific
embodiments, it is to be understood that this is for clarity and
convenience, and the disclosure herein includes all appropriate
combinations of information found throughout the specification. It
is to be understood that where a specific feature is disclosed in
the context of a particular embodiment or figure, such feature can
also be used, to the extend appropriate, in the context of another
figure, in combination with another feature, or in the invention in
general.
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